Generally, a collision detection device can be provided for a vehicle to detect a collision with the vehicle. For example, referring to JP-2004-212281A, a wire having a predetermined initial tension is arranged at a front side of a bumper reinforce member of the vehicle and extends in a vehicle width direction. A collision load exerted at the vehicle can be determined, by a detection of the tension variation of the wire in the collision of the vehicle.
Moreover, referring to JP-2004-156945A, a pair of leads extending in the vehicle width direction is disposed at a front portion of the vehicle. The collision of the vehicle can be determined according to whether or not the leads contact each other due to the collision.
Furthermore, referring to JP-7-190732A, an optical leakage fiber extending in the vehicle width direction is arranged at the front bumper of the vehicle. A light-emitting unit and a light-receiving unit are respectively disposed at two ends of the optical leakage fiber. When the optical leakage fiber is deformed or broken due to the collision of the vehicle, the light-receiving amount of the light-receiving unit is decreased. Thus, the collision of the vehicle can be detected.
On the other hand, a pedestrian is to be discriminated from other obstacles to be protected in the collision with the bumper of the vehicle. As described in JP-11-028994A, the pedestrian is distinguished based on a continuation time when the collision load (or deformation amount) exceeds a predetermined level. According to JP-11-310095A, the pedestrian is distinguished based on an increase rate of the collision load when the collision load exceeds a predetermined value. Moreover, referring to other art, the pedestrian is distinguished based on a peak value of the collision load. That is, according to these related arts, the pedestrian is discriminated from the other objects based on a predetermined variation component of a waveform of the collision load. In these cases, the collision load is to be corrected with respect to a velocity of the vehicle.
However, according to the device described in JP-2004-212281A, the tension of the wire which is arranged at the front side of the bumper reinforce member varies with time due to the stretch of the wire, so that a large detection error will be caused. In JP-2004-156945A, it is difficult to detect the value of the collision load, although the collision can be detected. According to JP-7-190732A, because the deformation of the front bumper is varied responding to a diversity of the collision, the deformation of the optical leakage fiber is various. Thus, it is difficult to appropriately detect the collision load although the collision can be detected.
In order to detect the collision load, a collision load sensor such as a strain gauge and an acceleration sensor, which output signals corresponding to the load, can be attached to the front surface of the bumper or the bumper reinforce member. Because the bumper extends in the vehicle width direction, it is difficult to appropriately detect the collision load exerted at the each part of the bumper. This problem may be solved by an arrangement of the multiple collision load sensors, which are disposed at the front surface of the bumper reinforce member and spaced from each other by a small gap in the vehicle width direction. However, because the manufacture cost is heightened to exceed the upper limit thereof, this method is practically impossible.